The organic electronic device refers to a device which requires charge exchange between an electrode and an organic material using holes and electrons. The organic electronic device can be largely classified into two types according to its operation principle as follows. One type is an electronic device having a configuration in which an exciton is formed in an organic material layer by photons flown from an external light source into the device and the exciton is separated into an electron and a hole, the formed electron and hole are transported to a different electrode, respectively and used as a current source (voltage source), and the other type is an electronic device having a configuration in which a hole and/or electron are/is injected into an organic material semiconductor forming an interface with an electrode by applying a voltage or current to two or more electrodes to allow the device to operate by means of the injected electron and hole.
Examples of the organic electronic device include an organic light emitting device, an organic solar cell, and an organic thin film transistor, which all require a hole injecting, hole extracting or hole transporting material, an electron injecting, electron extracting or electron transporting material, or a light emitting material for driving the device.
Hereinafter, the organic light emitting device will be mainly and specifically described, but in the above-mentioned organic electronic devices, the hole injecting, hole extracting or hole transporting material, the electron injecting, electron extracting or electron transporting material, or the light emitting material functions according to a similar principle.
In general, the term “organic light emission” means that electric energy is converted to light energy by using an organic material. The organic light emitting device (OLED) by the organic light emission has a structure usually comprising an anode, a cathode and an organic material layer interposed therebetween. Herein, the organic material layer may be mostly formed in a multilayer structure comprising layers of different materials, for example, the hole injecting layer, the hole transporting layer, the light emitting layer, the electron transporting layer, the electron injecting layer and the like, in order to improve efficiency and stability of the organic light emitting device. In the organic light emitting device having such a structure, when a voltage is applied between two electrodes, holes from the anode and electrons from a cathode are injected into the organic material layer, the holes and the electrons injected are combined together to form excitons. Further, when the excitons drop to a ground state, lights are emitted. Such the organic light emitting device is known to have characteristics such as self-luminescence, high brightness, high efficiency, low drive voltage, wide viewing angle, high contrast and high-speed response.
Various types of organic light emitting devices are known in the related art and they may be used for different applications. Examples of an organic light emitting device include a top light emitting OLED, a bottom light emitting OLED, and a dual-sided light emitting OLED.
If bottom light emitting OLEDs are used in active matrix displays, thin film transistors (TFT) are provided in front of the source of light emission, thereby reducing the ratio of the effective display area (aperture ratio). This problem is significant in the case when sophisticated displays having many TFTs are manufactured. With respect to a bottom light emitting OLED having an aperture ratio of less than 40%, an estimated aperture ratio of a WXGA type display that includes a TFT for 14″ grade is less than 20%. Such small aperture ratio negatively affects the driving power consumption and life-time of the OLED.
The above-mentioned problem can be prevented by using a top light emitting OLED. In a top light emitting OLED, an electrode that is not in contact with a lower substrate, that is, an upper electrode, is substantially transparent in a visible ray region. A transparent electrode that is used to form the upper electrode of the top light emitting OLED is formed of a conductive oxide, such as IZO (indium zinc oxide) or ITO (indium tin oxide). However, an electrode that is in contact with the substrate is typically made of metal. Similar to the top light emitting OLED, the dual-sided light emitting OLED includes a transparent upper electrode.
When fabricating the top light emitting OLED, after a metal electrode is deposited on a substrate, an undesirable native oxide layer is formed on the surface of the metal electrode. In detail, when the metal electrode is patterned by using photolithography and etching processes during the fabrication of an organic light emitting device, the metal electrode is exposed to moisture and oxygen, causing the native oxide layer to be formed on the metal electrode.
The native oxide layer reduces properties of the metal electrode, that is, inhibits the electron injecting or the hole injecting, thus reducing efficiency and luminance of the organic light emitting device.
One process to prevent the native oxide layer from being formed on the metal electrode is to form an organic material layer on the deposited metal electrode in situ. During the process, since the metal electrode is not exposed to air, the oxide layer is not formed on the surface of the metal electrode. However, it is costly and difficult to perform the process under vacuum. A raw material supplier sometimes supplies a substrate, on the surface of which a metal electrode is layered, while the substrate is exposed to air before an organic material is deposited.
Therefore, there is a need to develop an organic light emitting device having improved electron or hole injecting properties, even though the native oxide layer is provided on the metal electrode, and a method of fabricating the same. There is also the same need to develop the above mentioned organic electronic device.